Solid dielectric



Feb. l, 1944. F. M; CLARK `somD DxIELEcTRIc Filed March 31. 1942 a. www w #a frana-mums` .I AS www, m. ci uM/t ,mh s im is ...n

Patented Feb. 1, 1944 SOLID DIELECTRIC Frank M. Clark, Pittsfield, Mass., assignorl to General Electric Company, a corporation of New Yorlr Application March 31, 1942, Serial No. 436,929v

8 Claims.

The present invention relates to high Ifrequency electric devices, and in particular provides new and improved dielectric elements for such devices.

Hertofore, electric devices,- as for example ca-l pacitors and cables, when containing dielectric elements which were well adapted for operation at commercial frequency have been found to operate with undesirably high power factors at high frequencies, that is, frequenciesof the order f 100 to 5000 kilocycles.

. I have discovered that capacitor dielectric elements comprising solid, polynuclear, aromatic hydrocarbons, and in particular compounds of the polyphenyl type, function with good eiliciency and low power factors at high frequencies. Polyphenyl compounds, or mixtures comprising such compounds, as for example diphenyl, diphenyl oxide and diphenyl benzene (triphenyl), are preferred as high frequency dielectric elements. Compositions embodying my invention advantageously include by Weight at least about 25 per cent of diphenyl benzene.

In the accompanying drawing, Fig. 1 is a conventional representation of a high frequency generator containing, high frequency capacitors; and Fig. 2 shows conventionally a high frequency capacitor containing a dielectric element comprising one or more polyphenyl compounds.

Heretofore, mica and fused quartz have been considered the best availa-ble dielectric materials for the high frequency field. For various reasons it is desirable to employ a fusible organic material in place of mineral materials, such as mica and quartz.

Paraflinic hydrocarbons have been proposed as high frequency dielectrics, but .have been found to be unsuited because of their oXidizability. Oxidation products cause the power losses to be increased, the resulting heating in turn promotes further oxidation and thus eventual failureoccurs.

Aromatic hydrocarbons of the polynuclear class, and in particular compounds of this class which have a-suiliciently high molecular'weight to be substantially non-volatile over a working range of about 25-to ,100 C., not only are chemically sta-ble and havejgood dielectric constants. but such compounds 'arejoperable with power factors materially lower.;and less variable than mica. Such compounds are solids at room temperature.

While, in general, polyphenyl compounds or mixtures thereof lare preferred, itis advantageous for some purposes to employdielectric compositions comprising both u ncondensed polynuclear hydrocarbons, such as the polyphenyl group and condensed polynuclear' hydrocarbons, such as naphthalene.

Fig. 1 shows a high frequency circuit comprising as essential elements supply lines 2, 3 connected to a source of direct current (not shown) and leading to -an oscillation circuit to be described. Connected across the circuit 2, 3 are vacuum tubes 5, 6 comprising each as usual a cathode 'I, an anode 8 and a grid 9. The anodes are connected to the conductor 2. The cathodes are connected to the conductor 3 through a filament heating transformer I0. Both the conductor 3- and a neutral point of the secondary winding of the-transformer I0 are grounded as indicated. The secondary of the transformer I0 is connected 4by the conductors II7 I2 to lament heating circuit I3, I4. The rgrids each are connected to the conductor I6 leading to the oscillation circuit. The latter comprises high frequency capacitors I'l, I8 connected in series to the conductors 2 and I6, and grounded at the midpoint by a conductor I 9. The conductors 2 and I6 are connected also to an inductance coil 20 in series with blocking capacitors 2|, 22. A high frequency work circuit 23, 24 is connected in any convenient Way to the oscillation coil 20.-

High frequency capacitors, such as the capacitor shown in Fig. 2, may comprise interleaved armatures 23, 24 separated by a dielectric medium and connected to the terminals 25, 25' by the conductors 26, 26'. The dielectric medium has been indicated for the sake of clearness only yby the label Polyphenyl compounds. The enclosing casing has been omitted in the interest of simplication.

In accordance with my invention high frequency capacitors are provided with a composi tion either consisting wholly of one or more polyphenyl compounds or containing such compounds associated with other aromatic compounds, pr ferably of the. polynuclear type. Such compounds are to lbe understood as being unmodified, thatl is, uncombined with halogen or other substituted element or group. An example of such a composltlon is the following three-component mitture:

Parts Trlphenyl (diphenyl benzene) 2 Diphenyl 1 Naphthalene l The dielectric strength of this composition varles from about 42 kilovolts at 50 C. to about 43.5 kllovolts at C. The melting point determined by the ball and ring method is about 82 C.

Instead of naphthalene, other condensed polynuclear hydrocarbons such as anthracene and phenanthrene may be associated with the polyphenyl.

Instead of three-component mixtures described above, various two-component compositions of the polyphenyl type may be used, as for example mixtures of (1) diphenyl and triphenyl (diphenyl benzene) and V(2) diphenyl and diphenyl oxide. Other polyphenyl compounds are produced in the manufacture of diphenyl such as the tri, tetraand pentaphenyl. Such mixtures can be used without separation of their components as dielectric materials for high frequency capacitors in l accordance with my invention.

The following table indicates the variation in melting point of several compositions ofv diphenyl and triphenylall of which are capable of use as high frequency dielectric materials:

Table I Percent Per fmt diphenyl pheny ssa@ ' Table II shows the melting points of several compositions comprising triphenyl and diphenyloxide:

` Table II Per cent Per cent tridiphenyl Megitlg phenyl oxide p In some cases it is permissible to use two-component'mixtures of a polyphenyl and another unlike polynuclear aromatic hydrocarbon. Examples of such compositions are mixtures of 25 Darts by Weight of triphenyl and 75 parts by weightof naphthalene, having melting point of 10 8 C., equal, 'parts by weight of these components'having Amelting point of '75 C., and composition of 'I5 parts vby weight triphenyl and 25 parts by weight of naphthalene. The latter melts at 67 C.

The above examples are illustrated only. A wide latitude of dielectric materials, including two or more components of polyphenyl compounds, is within the scope of my invention. For

instance, instead of the percentages of the threecomponent mixtures first given above, I may use a. mixture consisting by weight of 40 per cent triy phenyl, 35 per cent diphenyl and 25 per cent 1000 kilocycles, such compositions operate with power factors below .01 per cent. Such materials have a dielectric strength of 30 kilovolts or higher over the ordinary working temperature range of 30 to 100 C.

In Fig. 3 are shown for comparison purposes power factors in per cent at 30 C. over a high frequency range of to 1000 kilocycles of mica (curve 30), of triphenyl (curve 3i), and of a mixture of 70 per cent diphenyl and 30 per cent diphenyl oxide (curve 32). The per cent power factor characteristic at this temperature of diphenyl and diphenyl oxide closely approximates these values. The per cent power factor of diphenyl, for example, is indicated by the following values:

Frequency Percent m power kilocycles factor 14o .041 40o .002 55o .002 55o .co2 soo .co3 1.000 .oor t The values for diphenyl oxide are as follows:

In Fig.v 4 are shown for comparison. purposes the per cent power factors over the same frequency range, but at 75 C. for mica (curve 33) and triphenyl (curve 3l). In both instances the power factor of the latter medium is less variable and of lower relative value than mica. The char-A acteristics of a composition consisting of a mixture of 30 per cent diphenyl. oxide and 70 per cent diphenyl are of the same order of magnitude. For example, the per cent power factor of the latter composition at 75 C. is in a range of .014 at kilocycles to .001 at 1000 kilocycles.

What I claim as new and desire to secure by Letters Patent of the United States is:

1.V A solid dielectricI composition suitable for use in electric capacitorsv consisting of diphenyl benzene, diphenyl and a condensed polynuclear hydrocarbon. I

2. A solid dielectric composition for use in i electric capacitors consisting by weight of about two parts of diphenyl benzene, about one part diphenyl and one part naphthalene. I

3. A solid dielectric composition suitable for use in high frequency capacitors consisting essentially of a diphenyl .benzene and anthracene. v l

4. A solid dielectric composition suitable Yfor use in high frequency capacitors consisting es,- sentially -by weight of about one part of diphenyl benzene and about three parts of naphthalene. 5. Solid dielectric compositions which are suitable for use in high frequency capacitors comprising mixtures of unlike poLvnuclear aromatic hydrocarbons, one of said hydrocarbons being diphenyl benzene, the latter constituting at least about 25 per cent podtion.

by weight of the entire com;

tric strength of about 42 kilovolts ,at 50 C. and a melting point of about 82 C.

8. A solid dielectric composition suitable for o use in high frequency capacitors including di- A5 phenyl benzene and diphenyl as substantial and essential ingredients.

FRANK M. CLARK. 

